Quoting Legoguy (Reply 4):Will any of the other older 737 models recieve winglets such as the 400 and 500 series?

No customer has yet signed up for winglets on -400s, but I wouldn't be surprised to see that happen sooner or later, albeit definitely in smaller numbers than the 733, and most likely also in lower numbers than the 735.
That said, which carriers are there that actually operate larger fleets of 734s (aside from AS)?

Isn't JL planning on retiring them in favor of 738s though? Obviously then adding winglets would not make too much sense. Though given that JL mostly uses them domestic, winglets would probably not give them any advantages to begin with.

Quoting DAL767400ER (Reply 13):Isn't JL planning on retiring them in favor of 738s though? Obviously then adding winglets would not make too much sense. Though given that JL mostly uses them domestic, winglets would probably not give them any advantages to begin with.

On that vein, JAL just took delivery of its first 737NG, a 737-800 with winglets. This is the first of many to come (30 I believe), so it's obvious they were able to justify the addition of winglets to the fleet.